1. Field of the Invention
The present invention relates to an electrophotographic photoconductor superbly resistant to natural light and short-wavelength light, used in an electrophotographic printer, copier, etc.; a process cartridge using the electrophotographic photoconductor; and an image forming apparatus using the electrophotographic photoconductor.
2. Description of the Related Art
For an electrophotographic photoconductor (hereinafter also referred to simply as “photoconductor”), a function of maintaining surface charge in a dark place, a function of receiving light and generating charge and a function of receiving light and transporting charge are necessary. Electrophotographic photoconductors are broadly classified into so-called single-layer photoconductors in which these functions are performed by one layer, and so-called functionally divided laminated photoconductors in which a layer mainly contributing to charge generation and a layer mainly contributing to maintenance of surface charge in a dark place and charge transfer upon receipt of light are formed one on top of the other in a functionally divided manner.
To electrophotographic image formation performed using these photoconductors, the Carlson method is applied, for example. In the Carlson method, image formation is as follows: a photoconductor is charged in a dark place by means of corona discharge, a latent electrostatic image based upon a letter/character, a drawing, etc. in a document is formed on the surface of the charged photoconductor, the formed latent electrostatic image is developed with toner, and the developed toner image is transferred and fixed onto a support such as paper. After the transfer of the toner image, the photoconductor is subjected to charge elimination, removal of residual toner, charge elimination by light, etc. and then reused. In recent years, along with the advancement of digitalization in electrophotographic processes, exposure with lasers whose input wavelengths to photoconductors are in the near-infrared range or with LEDs has been utilized not only in the field of printers but also in the field of copiers.
Also regarding photoconductors, electrophotographic photoconductors using organic materials have been put to practical use because they are advantageous in term of flexibility, thermal stability, layer formability and so forth. These days, functionally divided laminated photoconductors are very popular, each of which includes a photosensitive layer composed of a charge generating layer containing a charge generating agent and of a charge transporting layer containing a charge transporting material. In particular, negatively charged photoconductors are very frequently proposed, each of which includes as a charge generating layer a layer obtained by dispersing an organic pigment as a charge generating agent into a vapor-deposited layer or a resin and also includes as a charge transporting layer a layer obtained by dispersing an organic low-molecular compound as a charge transporting material into a resin.
Organic materials have advantages which inorganic materials do not have in many respects; nonetheless, organic materials which can sufficiently satisfy all properties required for an electrophotographic photoconductor have yet to be obtained. Specifically, degradation of image quality is caused by a decrease in charge potential, an increase in residual potential, change in sensitivity and the like which are due to repeated use. Although not all causes of the degradation have been ascertained, one major cause is the light resistance of a photoconductor. Generally, a photoconductor is stably resistant to near-infrared light used for exposure, etc. It should, however, be noted that when a paper jam occurs in a machine or maintenance including replacement of parts, etc. takes place, the photoconductor will be exposed to outside light. This outside light will be far greater in quantity than the light applied inside the machine and include a great deal of short-wavelength light which can damage the photoconductor. The photoconductor thus exposed to the outside light presents such problems as a decrease in charge potential and an increase in residual potential. To protect the photoconductor from the damage done by the outside light, a yellow fluorescent lamp with reduced short-wavelength light is used when the machine is assembled.
As for photoconductors themselves, addition of an ultraviolet absorber and/or an antioxidant to a photosensitive layer, addition of a compound having a maximum light absorption wavelength in the range of 380 nm to 480 nm to a photosensitive layer, and so forth have been proposed (refer to Japanese Patent Application Laid-Open (JP-A) Nos. 58-163946, 10-048856 and 11-184108).
However, these proposals are problematic in that the added compounds themselves cause a reduction in charge potential and an increase in residual potential.
JP-A No. 2007-271962 proposes a stable single-layer electrophotographic photoconductor which is highly sensitive and can withstand temporal degradation, obtained by combining a specific electron transfer material with a specific hole transfer material made of oxytitanium phthalocyanine. In this proposal, however, neither use of an electron transfer material as a light-resistant agent nor a way of doing so is disclosed or suggested, and there is such a problem that sufficient resistance to light cannot be yielded because the photoconductor has a single layer structure.
Accordingly, in reality, swift provision of the following is hoped for: an electrophotographic photoconductor which can adapt to reduction in the diameter of the photoconductor and a process with high circumferential speed, caused by miniaturization and/or increase in the speed of an image forming apparatus, and which is superior in light resistance; a process cartridge using the electrophotographic photoconductor; and an image forming apparatus using the electrophotographic photoconductor.